This invention relates to threaded fastening assemblies, and more particularly to such assemblies which are adapted to attach articles to soft material, such as gypsum based roofing material or light weight concrete. Applications contemplated by the present invention include the attachment of rigid insulation to previously existing roof structures. Prior art methods of attaching such insulation have included the use of toggle bolts with pre-drilled holes. The use of toggle bolts, however, presents a problem in roofing repair in that the formation of a hole through the roofing material causes residue to be deposited on the inside of the structure. The falling residue from the drilling operation can interfere with operations carried on within the structure. Another disadvantage of the toggle bolt method is that toggle bolts are generally quite expensive fasteners because they are comprised of a plurality of moving parts.
An object of the present invention is to simplify the attachment of roofing insulation to existing structures.
Another object of the invention is to provide a simplified fastener for attaching articles to soft material.
Another object of the present invention is to provide an inexpensive method of assembling a plurality of threaded elements together with a washer.
These and other objects of the invention are achieved with a fastening assembly which includes an elongated screw having a shank with a head at one end and threads at the other end. An enlarged anchoring element is affixed to the threaded end of the fastener. The anchoring element is a generally cylindrical body having an axial bore in one end and a screw thread disposed on its exterior. The screw thread on the anchoring element has a crest diameter generally twice as large as its root diameter. The anchoring element is preferably a molded part to facilitate the formation of a very high thread. The fastening assembly further includes a washer element captivated between the screw and the anchoring element. The washer has an outer diameter greater than the crest diameter of the anchoring element, and an inner diameter generally less than the head of the screw. The fastening assembly may further be used with a second washer having a large lateral extent to facilitate the attachment of relatively weak insulation material.